This invention relates generally to a multi-cavity injection molding apparatus for five layer molding and more particularly to such apparatus having actuating mechanisms for reciprocating elongated valve members between four different positions.
Multi-cavity injection molding apparatus for making five layer protective containers for food or preforms or parisons for beverage bottles are known. Two layers of a barrier material such as ethylene vinyl alcohol copolymer (EVOH) or nylon are typically molded between two outer layers and a central layer of a polyethylene terephthalate (PET) type material. However, this has previously been done by sequentially injecting first the PET, then the barrier material and finally the PET again. While this is satisfactory for some applications, sequential molding has the disadvantage that it requires relatively expensive tooling.
Valve gated multi-cavity injection molding apparatus having elongated valve members which reciprocate are also known. For instance, U.S. Pat. No. 4,657,496 to Ozeki et al. which issued Apr. 14, 1987 shows an actuating mechanism having an outer piston reciprocating in an outer cylinder and a inner piston reciprocating in an inner cylinder. The inner piston drives the elongated valve member and the outer piston drives a stem surrounding the elongated valve member and they operate in a controlled injection cycle to sequentially mold three layer products. None of the prior art actuating mechanisms are capable of reciprocating the elongated valve members between four different positions according to the present invention to provide five layer molding by simultaneous injection.